#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int sum(int n)
{
    if (n <= 2)
        return n;
    else
        return sum(n - 1) + sum(n - 2);
}

int main() {
    int n = 0;
    scanf("%d", &n);
    int ret = sum(n);
    printf("%d", ret);
    return 0;
}